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Modelling of nonlinear effects and the response of ultrasound contrast micro bubbles: simulation and experiment
Institute of Biomedical Engineering, Kaunas University of Technology, K. Donelaicio st. 73, Kaunas LT-3006, Lithuania.
Institute of Biomedical Engineering, Kaunas University of Technology, K. Donelaicio st. 73, Kaunas LT-3006, Lithuania.
Linköping University, The Institute of Technology. Linköping University, Department of Biomedical Engineering, Physiological Measurements.
Faculty of Science and Engineering, Vestfold University College, P.O. Box 2243, N-3103 Tønsberg, Norway.
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2004 (English)In: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 42, no 01-Sep, 301-307 p.Article in journal (Refereed) Published
Abstract [en]

The propagation of diagnostic ultrasonic imaging pulses in tissue and their interaction with contrast micro bubbles is a very complex physical process, which we assumed to be separable into three stages: pulse propagation in tissue, the interaction of the pulse with the contrast bubble, and the propagation of the scattered echo. The model driven approach is used to gain better knowledge of the complex processes involved. A simplified way of field simulation is chosen due to the complexity of the task and the necessity to estimate comparative contributions of each component of the process. Simulations are targeted at myocardial perfusion estimation. A modified method for spatial superposition of attenuated waves enables simulations of low intensity pulse pressure fields from weakly focused transducers in a nonlinear, attenuating, and liquid-like biological medium. These assumptions enable the use of quasi-linear calculations of the acoustic field. The simulations of acoustic bubble response are carried out with the Rayleigh-Plesset equation with the addition of radiation damping. Theoretical simulations with synthesised and experimentally sampled pulses show that the interaction of the excitation pulses with the contrast bubbles is the main cause of nonlinear scattering, and a 2-3 dB increase of second harmonic amplitude depends on nonlinear distortions of the incident pulse. (C) 2004 Elsevier B.V. All rights reserved.

Place, publisher, year, edition, pages
2004. Vol. 42, no 01-Sep, 301-307 p.
Keyword [en]
ultrasound, simulation, nonlinear, contrast agents
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-46245DOI: 10.1016/j.ultras.2004.01.023OAI: oai:DiVA.org:liu-46245DiVA: diva2:267141
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
In thesis
1. On Nonlinear Acoustics in Contrast Echocardiography
Open this publication in new window or tab >>On Nonlinear Acoustics in Contrast Echocardiography
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Ultrasound is one of the most commonly used noninvasive medical imaging techniques. Ultrasound contrast agents (UCA), consisting of encapsulated gas-filled microbubbles, have shown to increase the diagnostic precision in selected low echogenic patients. UCA also holds promise for bedside evaluation of myocardial perfusion quantification, but is not yet reproducible and specific enough for clinical use. In addition risks have been addressed when used, as first recommended, together with high mechanical index (MI) for reperfusion assessment by contrast destruction. We clinically observed increased myocardial velocities after UCA-administration when applied simultaneously with color tissue Doppler imaging (CTDI) arising the question if this increase was due to physiological factors or physical changes in the backscattered signals when UCA were present.

The aims of the thesis was to explain this velocity shift and simultaneously to contribute to a future safe and contrast specific application by further characterizing the non-linear acoustic properties of UCA when located in an acoustic field. Of specific interest was to evaluate in which way nonlinear wave propagation affects the response from UCA and if a change in pulse shape, length or polarity can be utilized to increase the nonlinear signal contribution.

Twelve patients with ischemic heart disease were examined with CTDI before and after UCA-administration in order to verify the change in peak systolic velocity. An experimental in vitro model including flow and tissue phantoms for UCA was established for CTDI. Raw data from single-element transducers and clinical ultrasound systems were collected for three different UCA and analyzed to determine if the observed velocity shift could be reproduced in vitro and to find a possible cause. Our results show in vivo and in vitro that UCA will affect the autocorrelation phase shift estimator used for CTDI in terms of contribution from rupturing UCA microbubbles, which explains the velocity shift. CTDI during contrast infusion should therefore be avoided unless it can be performed at low MI where the majority of the UCA are intact.

The computational model for spatial superposition of attenuated waves was modified to include an operator for pulse distortion from nonlinear wave propagation. The Matlab™ toolbox Bubblesim based on a modified Rayleigh-Plesset-equation and with insonation parameters such as frequency, pressure amplitude, pulse length and polarity was used to study the response from single microbubbles either for simulated pulses or for pulses generated by clinical ultrasound systems and single element transducers. The combination of the two models also provided a computational platform to asses pulse distortion from nonlinear wave propagation, the response of the UCA bubble and the linear backscatter of the low amplitude bubble echo. When evaluating the harmonic response in simulations and in vitro, the interaction of the excitation pulses with the contrast bubbles was identified as the main cause of nonlinear scattering, and a 2-3 dB increase of the second harmonic amplitude depends on nonlinear distortions of the incident pulse. By applying small changes of short (<3.5 cycles) and fragmented transmitted wideband pulses of 2-2.5 MHz, it is shown that inverted pulse polarity considerably modulates power without affecting a low and safe MI (<0.4), and the results lodged promise to further to enhance a contrast response.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 114 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1338
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-65418 (URN)978-91-7393-315-5 (ISBN)
Public defence
2010-11-12, Eken, Campus US, Linköpings universitet, Linököping, 09:15 (Swedish)
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Available from: 2011-02-07 Created: 2011-02-07 Last updated: 2011-02-07Bibliographically approved

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Ressner, MarcusJanerot Sjöberg, BirgittaAsk, Per

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